In recent years, various oncolytic virotherapy techniques involving the use of viruses for treatment of cancer have been developed. Examples of viruses used for such therapy include adenoviruses, retroviruses, and vaccinia viruses.
Because of wide host range and high expression efficiency, in recent years, vaccinia viruses have been used as polyvalent vaccines for infectious diseases (e.g., HIV and SARS) in the form of expression vectors into which foreign genes have been introduced.
In addition, a technique for treatment of cancer making use of the oncolytic properties of vaccinia viruses has been reported (see Patent Document 1).
Separately, the vaccinia virus growth factor (VGF) gene and the O1L gene have been reported as genes that activate ERK in the infected cells and positively regulate the growth of vaccinia viruses (see Non-Patent Document 1). With respect to the VGF gene, it was reported that vaccine pathogenicity would be reduced via deletion of the VGF gene (see Non-Patent Document 2). Also, use of a vaccinia virus, which is deprived of the VGF gene and the TK (thymidine kinase) gene, for treatment of cancer, has been reported (see Patent Document 2 and Non-Patent Document 3).